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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
Read-across to the target chemial is claimed based on the category of stilbene optical brighteners as documented within the Category justification report attached to Chapter 13 of this dossier.
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
GLP compliance:
yes
Analytical monitoring:
yes
Buffers:
- pH 4: 0.1 mole acetic acid + 0.1 mole sodium acetat diluted to 1000 mL with water + 60 mL 1 N HCl
- pH 7: 0.041 mole di-sodium-hydrogen phosphate + 0.028 mole potassium di-hydrogen phosphate diluted to 1000 mL with water
- pH 9: 0.043 mole di-sodium tetraborate + 0.017 mole potassium di-hydrogen phosphate diluted to 1000 mL with water
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: Only brown glass reaction flasks are used
- Sterilisation method: The buffer solutions are heated before use at 121 °C for 15 minutes.

TEST MEDIUM
- Preparation of test medium: 0.05 to 0.06 g test substance is accurately weighed, dissolved and diluted to 250 mL with water
Preliminary study:
The tested substance is stable (hydrolysis <10 %) at pH 4, 7 and 9 at 50 °C
Transformation products:
not measured
Remarks:
as the substance is stable no transformation products are identified
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Remarks on result:
other: no St. dev. provided
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
Remarks on result:
other: no St. dev. provided
pH:
9
Temp.:
25 °C
DT50:
> 1 yr
Remarks on result:
other: no St. dev. provided

Description of key information

The substance is included in the category of Stilbene Fluorescent Whitening Agents (SFWA) comprising of 14 member substances in total. The category of Stilbene Fluorescent Whitening Agents is defined as a structurally related group of substances that are derivatives of 4,4’-bis(1,3,5-triazinyl-2-yl)amino)stilbene-2,2’-disulphonic acid, each with one aniline and one alkyl derivative amino moiety at the triazine ring. The aniline moiety can also be mono- or di-sulfonic aniline. With the exception of OB 3a-A (free acid) and OB 3a-A (NaK) all substances are sodium salts. The molecular structures of OB 3a-A (free acid), 3a-A (NaK) and 3a-A (Na) are the same except that the first one is the free sulfonic acid and the second one the potassium/sodium salt.


The chemical structures are highly symmetric with an extended chromophor system. Substituents have little influence on the chromophor system; they affect the application properties and substantivity.


To be included in the defined category of SFWA a substance must have the following characteristics:


 •           All substances are derivatives of 4,4’-bis(1,3,5-triazinyl-2-yl)amino)stilbene-2,2’-disulphonic acid, each with one aniline derivative (R1) and one alkyl derivative amino moiety at the triazine ring (R2)


•            The substances have all negative calculated log Pow (<-1), due to the fact that except from the acid form, they are all salts.


•            Molecular weights range from ca. 872 to ca. 1369 g/mol.


•            All category members are very soluble, with an individual solubility ranging from ca. 1 to >200 g/l. Water solubility tends to increase with the degree of sulfonation. They are all very stable and do not hydrolyse.


•            As a result of the stilbene portion of the molecule, common to all category members, these fluorescent whitening agents have an UV absorption maximum between 340 to 360 nm in water, which makes them subject to direct photo-degradation in the hydrosphere. The structural differences between the substances are determined by the presence of two moieties (R1 and R2) bound to both triazine rings. Each substance is characterized by a combination of two of these moieties to each triazine ring and by the cations of the sulfonic acid group present, which in almost all cases is Na+, in one case it is Na+ and K+; instead of these cations a proton (H+) is present for one substance. R1 is bound to the 3 position of the triazine ring and is described as an aniline function, which may have one or two sulfonate functions. Based on the variability related to R1 or R2 two different sub-categorizations can be considered; Sub-categorization based on R1 or Grouping based on R2. R2 can be constituted by the following:


•            morpholino


•            methyl (2-hydroxyethyl)amino,


•            2-hydroxyethylamino,


•            bis(2-hydroxyethyl)amino,


•            diethylamino


•            (2-carbamoylethyl)(2-hydroxyethyl)amino,


•            bis(2-hydroxypropyl)amino,


For read-across both of these structural differences in moiety R1 and R2 are taking into account.


Two existing reliable studies have been presented within the dossier: both studies (for OB 2 -A and OB 3a-MSA) demonstrate that the test substances are stable (hydrolysis <10 %) at pH 4, 7 and 9 at 50 °C and that the half-life of the tested substances for hydrolysis is proved to be greater than 1 year (Ciba-Geigy Ltd., 1992). For all structures it can be estimated that hydrolysis does not occur because there are not hydrolysable groups present in any of the structures. Hydrolysable organic groups are in fact those groups that can react with water like esters, anhydrides, amides, carbammates, nitriles, cyanates, epoxides, halomethanes, alkylhalides, urea.


Carbamoyl derivative can be considered having a hydrolysable functional group, since it is an amide derivative, which can be hydrolyzed to the acid form. This potential reaction, in any case does not lead to smaller reactive substances that can have an impact on the environmental fate different from the parent compound. A further potential hydrolysis reaction that can be expected for the category, but not in the environmental conditions, is the opening of the morpholino ring, reaction that doesn’t produce significantly different metabolites that can influence the environmental impact. Therefore, the existing studies results can be applied to all the substances of the category.

Key value for chemical safety assessment

Half-life for hydrolysis:
1 yr
at the temperature of:
25 °C

Additional information

The test substance is considered as stable (hydrolysis <10 %) at pH 4, 7 and 9 at 50 °C with the half-life for hydrolysis being greater than 1 year.